Structural Report on the Strength of the Amphibious Undercarrige for the Polaris FIB
Structural report on the strength of the amphibious undercarrige for the Polaris FIB
Purpose
This document is a translation of a preliminary working report that details the structural strength and integrity of the retractable amphibious undercarriage for the Polaris Flying Inflatable Boat. The analysis was performed by Anders Hansson, a qualified structrual engineer from a request by Peter Wicander, general agent for Polaris Flying Boats in Sweden.
Summary
This report confirms that the strength and structrual integrity of the amphibious undercarriage demonstrates sufficient strength to meet the requirements of JAR 22 articles 473,477,479,485 and 725.
Translation
The translation of this document from Swedish to English will only address the textual content of the report as the included diagrams are self explanatory. The translation will refer to each page in the document so that the reader can orientate him/herself with respect to the text on each page.
Page 2 (10)
Prerequisites
The analysis has been performed using Finita program ALGOR. The model of the undercarriage has been drawn using CAD program ALIBRE. The modelling uses the actual dimensions of the undercarriage but no modelling of details such as welds, eventual additionall welded brackets has been performed. The measurements and geometry of the undercarriage was recieved from the importer and measurements were even taken from the actual undercarriage. See attachement No1
Material information and data
The undercarriage is manufactured from titanium. Attachement No1 specifies material type as Titanium TG5. In a date sheet from a Swedish material supplier the stretch specifications are 0.2 =828 Mpa for that specific materials quality. The break specifications are b=895Mpa.
Main undercarriage
Geometry
The undercarriage is built up according to the diagram below:
...... Diagram ......
The undercarriage is mounted in the boat hulls stern with two mounting brackets. Both of the mounting brackets take the bending moment from the loading of the wheels. The horizontal axle on each leg goes through the two mounting brackets and meet in the middle of the joining tube . Both the left hand and right hand axles are fastened in the joining tube by three (per side) M6 bolts that go completely through the joining tube and undercarriage legs.
Page 3(10)
The analysis has been somewhat simplified by that, only the part of the undercarriage leg that is on the outside of the fastening bracket (which is attached to the hull) has been analysed. The horizontal undercarriage tube is assumed to be firmly supported by the mounting brackets.The analysed geomety of the landing gear is as detailed in the diagram below.
...... Diagram ......
Loading Case 1 – JAR22 article 473 479
This loading case describes a symetrical landing with a max all up weight of 450kgs. The vertical descent rate of the landing is reckoned to be 1.5m/s .
The load that shall affect the undercarriage is totally dependant upon the length of the energy absorbing load path. A simple summary of the load as a function of the load path has been detailed in the table below. The supposition is that a constant force stops the movement from 1.5m/s to standstill.
Sink rate m/s 1.5
Weight kg 450
Movement energy J 506
...... table ......
Verticle load N/ leg Vertical Load N total Load path mm Load factor
...... data in table ......
Page 4 (10)
The table below show a summary of the undercarriage legs deformation only in a bending and twisting plane of the horizontal axle. The summary has been performed using the handbooks method. In addition to this deformation one must include the wheels suspension and the bending of the undercarriage legs vertical tube.
Vertical load on the leg N Bending in mm twisting in mm total deformation mm
...... data in table ......
Based on the above conclusions a load path of 100mm has been assumed which results in a vertical force of Pv of 2500n per undercarriage leg. This load is combined according to JAR22.725 with a horizontal load Pii of 1443N
...... diagram of undercarriage leg ......
Page 5(10)
Load case 2 – JAR22 article 485
This load case describes an oblique landing where there is a sideways loading of the undercarriage leg. The vertical load Pv is 50% of the previous example and Pv=1250N. This load is combined with a side loading of Ps 750N. In load case ”a” the load is applied inside of the hull and load case ”b” presumes a load on the undercarriage leg from the outside.
...... diagram of undercarriage leg with loads ”a” and ”b” ......
Page 6(10)
Results
Load case 1 – Jar22 article 473 479.
The diagrams below show the stress distribution and the resulting deformation. The maximum stress lies under the defined load specifications of the material but with a low safety margin.
...... two diagrams showing the srtress and deformation in an undercarriage leg ......
Page 7(10)
Load case 2 – JAR22 article 485
The diagrams below show the stress distribution and resulting deformation. The maximum loading lies well under the deformation specification of the material.
...... two diagrams showing the srtress and deformation in an undercarriage leg .....
Page 8(10)
...... two diagrams showing the stress and deformation in an undercarriage leg .....
Page 9(10)
Bolts in the axlel joining tube
The strength of the bolting arrangement of the middle tube and undercarriage legs have been calculated for load case 1 according to the following suppositions and specifications.
Load in wheel centre N 2887
Moment arm mm 303
Moment mm 874 761
Tube diameter mm 30
Screw load N 29159
Bolt diameter mm 5
Load distribution area mm2 19.6
Bolt tension N/mm2 1485
The bolts used are assumed to be class 12.9 , have a break point of 1200 Mpa and a tensile strength of 1080Mpa. The load exceeds what a single bolt can take but with the assumption that the landing gears horizontal tube spreads the twisting load somewhat evenly between the three bolts, means that there is a good safety margin.
Nosewheel.
The nosewheels geometry is detailed in the picture below.The vertical loads are taken by a triangular structure onto the glass fibre hull. The sides of the nose wheel construction are strenghtened by metal webs. The load on the nose wheel is considerably lower than on the main gear and all of the moment arms are shorter.
It has been assumed that the load on the nose wheel is sufficiently low as not to be critical and no stress and deformation calculations have been performed.
...... picture of nosewheel ......
Summary
The analysis states that the analysed components of the undercarriage have sufficient strength. This is based on the assumptions that the material specification, load paths and load specifications are correct and that the construction technique is of sufficient qaualty.
Page 10(10)
Attachement 1
Diagram showing the attachement of the undercarriage legs and the dimensions used in the analysis.